1. Field of the Invention
This invention relates to heat bonding apparatus and, more particularly, to apparatus for heat bonding flexible printed circuits in a hydraulic press.
2. Description of the Related Art
The fabrication of printed circuit boards and flexible harnesses is carried out by assembling multiple layers of material and laminating them in a heat bonding press. The assembled layers to be laminated are placed between the plates of a pressure transfer plate assembly before heat bonding takes place. Various layers are built up on a set of workpiece-aligning pins which go through corresponding holes in the layers. A second set of pins is used to align the pressure plates with respect to each other. In previous arrangements of the plate-alignment pins, the removal and replacement of them was time-consuming and labor-intensive. The plate-alignment pins are ordinarily press-fitted into the bottom plate of the pressure transfer plate assembly, so that when one of them becomes bent, worn, or broken it is difficult to replace. Furthermore, the conventional arrangement for the workpiece-aligning pins leads to fairly rapid wear of the aluminum bottom plate by the pin in its hole, which leads to inaccurate alignment of the workpiece. It would be a great advantage in the art of laminating printed circuit boards and flex harnesses if an improved pressure transfer plate assembly were developed which obviated the two problems referred to above.
Some examples of the related art are briefly discussed below.
U.S. Pat. No. 2,330,577 to Hampf relates to a centering device for the cutting of sheet metal disks in which the cutting members are stationary while a rotary movement is imparted to a plate during the cutting operation about the center of a pointed pivot. The centering pivot and the bed or matrix pertaining thereto are arranged on pins adapted to be turned about the central axis, with the pins being mounted in corresponding parts of the machine frame such that an axial movement imparted to the pins brings them toward one another when they are turned in the same direction. The pins tend to clamp the piece of sheet metal between the pivot and the bedding in the process of cutting to prevent play.
U.S. Pat. No. 2,372,716 to Evans relates to a locating key device by means of which a jig, tool, or other fixture may be mounted upon a table having a slot or groove therein to receive a portion of the key which projects from the fixture, the key being of such formation that by turning it to adjusted positions it may accommodate itself to tables having slots of different widths.
U.S. Pat. No. 2,389,184 to Cook relates to releasable clamping and securing devices for use in drill jigs and similar type fixtures. A plurality of spaced clamping devices is provided to clamp a top plate against a workpiece. Each clamping device comprises generally a threaded member or a bolt on the plate, a pin fixed in the plate, and a cam element in threaded engagement with the bolt and cooperable with the pin.
U.S. Pat. No. 2,576,003 to Dry is directed to an alignment bolt for use by an automobile mechanic in replacing an engine gasket. A plurality of such bolts are used to maintain the gasket in alignment with the crankcase and oil pan. Each bolt is provided with a threaded end for threaded engagement with the threaded openings of a flange. The bolt includes a cylindrical portion adjacent the threaded end thereof and a cylindrical head formed on the other end of the bolt with a diameter greater than the cylindrical portion. The exterior surface of the head is knurled to facilitate manual turning of the bolt. The head is also provided with a transversely extending slit or kerf for the reception of an end of a screwdriver for tightening the bolt. Positioned on the cylindrical portion of the bolt is a tapered conical helical or coil spring with a portion arranged in abutting relation to the head and one end secured in a socket of the bolt.
U.S Pat. No. 2,707,419 to Schron is directed to means for locating fixture plates with respect to the beds or platens of machine tools. A combination is provided of a fixture plate having circular openings therein, and fixture keys having circular shanks disposed in the openings and heads of various polygonal shapes centrally disposed relatively to the shanks and depending from the fixture plate. These keys are adapted for movement in the T-slots or grooves of the bed or platen of machine tools, such as milling machines.
U.S. Pat. No. 3,540,128 to Giles is directed to a ready-built base plate having a precision-made pattern of holes in it that are equally spaced and with a central slip hole or register. The pattern of holes provides quick and proper location and positioning of parts to be machined. The base plate is so constructed as to permit various accessories secured to the plate by means of bolts from the face side of the plate as well as from the bottom side, all the while using the same hole in the same location. The base plate may be used with various locator devices, in particular a device comprising a body, three locating rods, a tapered pin, and four screws. The body has a hole through it which is threaded on one end, and three other holes, each of which is equally spaced at 120.degree. to receive locating rods. The locating body is equipped with a shank which is received by the register hole of the plate. The locating body further receives a tapered pin which can be moved in or out by means of a setscrew threaded at the end of the body. As the tapered pin is pushed into the body by adjusting the setscrew, it pushes out locating rods on the top of the body to the desired position.
U.S. Pat. No. 3,746,488 to Messenger is directed to an apparatus for removable holding mold cavity sections to mold plates, wherein the mold plate includes a regular, rectangular array of identical, cylindrical openings extending perpendicular to the plane of the plate and partway therethrough, the openings being arranged in a plurality of rows and columns with the openings being equally spaced apart in the rows and columns. Each of the mold cavity sections has a cylindrical extension adapted to fit into the openings. The mold plate also includes a plurality of slots therethrough perpendicular to the openings and with the edges of the slots slightly overlapping the openings. A plurality of retainer keys or slide bars are slidably positioned in the slots for matingly, lockingly engaging mating keyways or grooves in the mold cavity extension. The slide bars have notices or recesses in their side edges corresponding to the shape of the openings such that they can be moved a short distance, where the recesses register with the openings, for releasing the mold cavity sections without necessitating removal of the slide bar entirely from the plate.
U.S. Pat. No. 3,942,780 to Clement is directed to a drilling or milling machine on which workpieces of thin metal plate can be accurately located for machining. A table formed with openings in regular matrix array occupied by plates at least some of which are apertured is secured to a work plate. A workpiece is located on a rectangular workpiece support plate and clamped thereto. The support plate has two bores, each housing a spring-loaded pin and each adjacent to an opposite corner of the support plate. The pins fit into the respective bores and into adjacent plate apertures of the matrix and are engaged by slotted plates. When moved in one sense the plates pull the pins down against the spring loading to clamp the workpiece support plate and table together, and when moved in the opposite sense allow the pins to release by the spring action so that the workpiece support plate can be removed.
U.S. Pat. No. 4,191,366 to Rabin is directed to a universal planetary clamping device. The base surface of a rigid plate rests upon the work support surface of a machine tool. An insert having an aperture therethrough is journalled within the plate. A pin is detachably affixed to a workpiece and extended through the aperture. Access is provided through the edge of the plate for engaging the pin to the insert and for cammingly advancing and retracting the insert relative to the base surface. The workpiece is drawn against the work bearing of the plate in response to advancement of the insert. Random aperture location to accommodate several randomly placed pins is provided by a plurality of rotatable journalled inserts, each having a slotted aperture.
U S. Pat. No. 4,431,474 to Gronek et al is directed to a thermocompression bonding assembly particularly adapted to bond an array of miniaturized electrical leads to a corresponding array of respectively aligned pads of a metallized circuit. The assembly includes an internally heated bonding thermode that is uniquely secured to only a single, resiliently mounted support rod which forms part of a specially constructed hanger or support assembly. The support assembly includes a platen-mounted, reciprocally displaceable die set, comprising an upper internally cooled metal plate, an intermediate insulative plate, and a lower metal plate formed with two downwardly extending and longitudinally spaced pairs of thermode alignment and backup support brackets The lower plates also include a plurality of downwardly protruding ribs that define horizontally disposed reference alignment points for establishing precise parallelism between the thermode and the support assembly.
U.S. Pat. No. 4,500,079 to Morghen is directed to a removable and replaceable locating pin adapted to locate a workpiece on a tooling fixture for machining thereof. The locating pin includes a locator element having various configurations adapted to cooperate with a workpiece for positioning the workpiece in various directions of restraint. The locating pin is provided with manually actuatable locking means that permits easy adjustment or removal of the specific locator element as a particular machining operation may require.
U.S. Pat. No. 4,506,442 to Alzmann et al is directed to apparatus for stacking a plurality of laminate layers in registered superposed relation to enable the layers to be joined to form a composite board. A table has a surface on which a plurality of laminate layers can be successively stacked in aligned superposed relationship on pins slidably received in respective apertures in the table. The pins rest on support members carried on a lower support table mounted beneath the surface of the table on which the layers are stacked. The lower support table is raised relative to the stack of layers after successive layers have been placed on the pins so that a given projection of the pins from the laminate layers will be obtained.
U.S. Pat. No. 4,598,453 to Wills is directed to a planar workpiece such as a printed circuit board or a ceramic substrate for an integrated circuit which is aligned by apparatus including three pivotal cams that initially fit relatively loosely in three apertures in the workpiece. As the cams are rotated, they contact the sides of the apertures and thereby urge the workpiece into a centered and aligned position.
None of the patents described briefly above discloses a pressure transfer plate assembly for an apparatus to heat bond flexible printed circuits in a hydraulic press that allows the bonding of twice the amount of 15".times.16" flex harnesses as is now possible with existing bonding tools, with only a modest increase in labor expenditure. None of the patents describes a lamination bonding tool that will outlast current bonding tool designs by retrofitting the pin position countersink holes with steel inserts and providing the top plate locating pins with threads for easy removal and installation.